The Characterization of Irradiation Damage in Reactor Graphite Using High Resolution Transmission Electron Microscopy an
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The Characterization of Irradiation Damage in Reactor Graphite Using High Resolution Transmission Electron Microscopy and Raman Spectroscopy A. N. Jones1, L. McDermott1 and B. J. Marsden1 1 Nuclear Graphite Research Group, Research Centre for Radwaste & Decommissioning, School of MACE, University of Manchester, UK ABSTRACT Nuclear graphite components are produced from polycrystalline artificial graphite manufactured from binder and filler coke material with approximately 20% porosity. During the operational lifetime of a nuclear reactor the graphite moderator is subjected to fast neutron irradiation which contributes to changes in material and physical properties such as thermal expansion co-efficient, young’s modulus and dimensional change. These changes are directly driven by irradiation induced changes to the crystal structure as reflected through the bulk microstructure. Therefore it is important that irradiation changes and there implications on component property changes are understood. Work carried out under the FP7 CARBOWASTE consortium under work package three is underway to characterize both structural and radiological damage in graphite. This study examines a range of irradiated graphite samples removed from the British Experimental Pile Zero (BEPO) reactor. Raman spectroscopy and Transmission Electron Microscopy (TEM) have been used to compare the effect of increased irradiation Fluence on graphite microstructure. Irradiation induced crystal defects and changes in crystallite size are observed using TEM and related to Raman Spectroscopy, comparisons are also made to virgin nuclear grade graphite. INTRODUCTION Graphite was chosen as the material of choice as moderator and neutron reflector material in more than 100 nuclear power plants, research and plutonium-production reactors [1,2] due to its ability to slow down the neutrons produced by the nuclear fission reaction, as a result of its high scattering and low neutron capture cross-section. Graphite has good mechanical strength and good thermal properties enabling it to provide channels for fuel and control rods and provide a large heat sink during thermal transients. However, the action of slowing neutrons by scattering leads to irradiation damage to the crystal structure through a series of knock-on collisions which results in defect formation within the graphite crystal the lattice [2]. During the operational lifetime nuclear graphite moderator component changes are directly driven by irradiation induced damage to the crystal structure as reflected through the bulk microstructure [3-5]. Understanding neutron damage and its implications on component property changes are important for future Gen IV reactor design, present operational lifetime and future decommissioning. This study examines a range of irradiated graphite samples removed from the British Experimental Pile Zero (BEPO) reactor in 1993. BEPO was commissioned in 1948 and closed in 1968, and was a prototype UK experimental pile aimed at gaining experience for the design and operation of the W
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